A color filter is an essential constitution unit in liquid crystal displays and solid-state image pickup devices.
Since a liquid crystal display is more compact and exhibits equivalent or better performance as compared to CRT which is widely used as a display device, the liquid crystal display has been increasingly used in place of CRT as a display device for a TV screen, a personal computer screen, and others. Further, in recent years, the trend of development in liquid displays has moved from a use in monitor with a relatively small screen which is demanded in the past to a use in TV with a large screen and high image quality.
As for the color filter for liquid crystal displays (LCD), a substrate is increased in its size in manufacturing a large TV. For a curable composition which is used in preparing a color filter employing such the large substrate, curability at low energy has been desired for improving the productivity.
Further, for liquid crystal displays for a use in TVs, better image quality than those used for monitors in the past has been demanded. That is, the improved contrast and color purity have been demanded.
For the curable composition used in preparing a color filter, a coloring agent (organic pigment or the like) having a further finer particle size has been demanded for a use for improving the contrast (for example, see JP-A No. 2006-30541).
However, when the pigment adsorption of a dispersing agent is promoted to improve the dispersion stability upon including a pigment having a small particle size in a curable composition, the dispersing agent bridges between pigments thereby promoting a pigment aggregation, and thus the storage stability such as dispersion stability, or the developability when forming patterns with the use of the curable composition tend to deteriorate.
In addition, since making the pigment finer increases the surface area, the use of finely made pigment tends to increase the adding amount of dispersing agent for a pigment dispersion in the curable composition.
Further, when a better acid value of resin to be added at the time of dispersion is provided for attaining developability, the pigment aggregation tends to be promoted due to an interaction of a hydrogen bond between acid groups or the like.
When a resin is added to a curable composition after the pigment dispersion for attaining the developability, the resin is required to be added in a large quantity.
For a curable composition used in preparing a color filter, further higher content of a coloring agent (organic pigment) in a solid content has been demanded for improving the color purity. However, when a coloring agent is included in a curable composition at high concentration, since the content of photopolymerization initiator and photopolymerizable monomer in a curable composition is reduced, a problem arises in that the curability is hardly attained in an exposed part (even if the) while curability at low energy is desired for the curable composition.
In addition, for a curable composition which is used in preparing a color filter for solid-state image pickup devices, curing with low energy has been also desired. With respect to the color filter used for solid-state image pickup devices, a colored pattern is made finer and accordingly the pigment density in the composition is improved.
Further, in the pigment-based color filter, the content of pigment dispersing agent in a curable composition is more likely increased due to a pigment refinement for reducing the color irregularities caused by relatively coarse pigment particles. As in the curable composition used for manufacturing LCD, the increase of pigment dispersing agent content in the curable composition tends to deteriorate the storage stability such as dispersion stability, or the developability when forming patterns with the use of the curable composition, and also leads to a problem such that the curability is hardly obtained.
In order to deal with the problems such as color irregularities in colored patterns formed, a technique of using an organic solvent-soluble dye instead of pigment as the coloring agent has been proposed (for example, see JP-A No. 2-127602). However, in the dye-based color filter, problems such as polymerization inhibitory effect derived from the dye or deteriorated storage stability such as dye precipitation had become significant due to the increase in dye concentration.
As described above, various problems arise in the curable composition used for preparing a color filter that, for both the cases of use in liquid crystal displays and use in solid-state image pickup devices, the sensitivity is low and sufficient curability cannot be obtained because the concentration of coloring agent is increased while the content of the photopolymerization initiator and the photopolymerizable monomer which are the essential components for curing the curable composition are limited; adhesiveness to a substrate is insufficient; lowered development rate or residue formation in an unexposed part is observed; desired patterns are very hardly formed; dispersion stability and developability are deteriorated when the coloring agent used is a pigment; storage stability is deteriorated such as dye is precipitated, when the coloring agent used is a dye; and the like.
With respect to those problems, in the past, investigation on providing polymerizability to a resin which is introduced mainly to provide a film formability and developability thereby improving the sensitivity has been carried out (for example, see JP-A No. 2000-321763, JP-A No. 2003-029018, “Color Filter new technology Trend (Color Filter Saishin Gizyutsu Doukou)” (published by JOHOKIKO Co., Ltd.) p 85-87, and “Advanced Technologies for LCD Color Filters (Saisentan Color Filter no Process Gizyutsu to Chemicals)” (published by CMC Publishing Co., Ltd.) p 129-150). In addition, technologies disclosed in such can be also mentioned. However, there are problems such as that the synthesis method for the resins is complicated, the synthesizable structure is limited, and the like. Also, satisfied light exposure sensitivity is not yet obtained although such resins are used. Since the light exposure sensitivity is not sufficient, curing in a deep area such as around a substrate interface is insufficient thereby causing a problem such as (deteriorated) substrate adhesion is deteriorated.
The present invention is made in the light of above considerations, and the objects of which is to provide a curable composition for color filter which exhibits highly sensitive curability, excellent storage stability, and high sensitivity even in the case where a coloring agent, which absorbs active energy ray, is included at high concentration; a color filter which has less development residue on an unexposed part, excellent adhesiveness to a substrate of an exposed part, and desired pattern cross-sectional shape and highly precise colored patterns; and a manufacturing method excellent in the color filter productivity. The task is to achieve these objects.